The present invention relates to a power stack which is preferable used as a driving apparatus for an automotive electric rotary machine.
For example, the following prior art documents 1 to 4 respectively disclose a power stack including cooling members and semiconductor elements alternately laminated, according to which the semiconductor element is sandwiched between a pair of cooling members disposed in the laminating direction. The heat generated from the semiconductor element is absorbed by these cooling members. Therefore, the power stacks disclosed in the prior art documents 1 to 4 can prevent thermal breakdown of semiconductor elements.
1: Japanese Patent Application Laid-open No. 11-214599 (1999)
2: Japanese Patent Publication No. 7-3846 (1995)
3: Japanese Patent Application Laid-open No. 3-76256 (1991)
4: Japanese Utility Model Publication No. 6-10696 (1994)
However, the above-described prior art documents 1 to 4 disclose nothing about the layout of the semiconductor elements in the power stack. Therefore, according to the power stacks disclosed in the prior art documents 1 to 4, the power stack will have bad cooling balance as a whole when the semiconductor elements have different heat generation rates.
More specifically, the heat generation rate of the semiconductor element depends on electric output power, conduction time, and operation timing of a controlled object device. This is the reason why the semiconductor elements have different heat generation rates. If the layout of semiconductor elements is determined without considering differences of heat generation rates, the power stack will have undesirably deviated distribution of heat generation rates as a whole. Having the undesirably deviated distribution of heat generation rates is not desirable because portions having higher cooling efficiencies and portions having lower cooling efficiencies appear locally in the power stack. In short, the power stack as a whole has a bad cooling balance.
Accordingly, there will be a possibility that semiconductor elements cannot be sufficiently cooled in a case that the layout of semiconductor elements in the power stack is improper.